With development of electronic products toward miniaturization and multi-function, the electronic products have increasingly higher requirements on energy density of a battery used thereby, which requires a cell of the battery to provide more capacity in the same space. In a secondary battery with a conventional wound type cell, both of a starting end of a positive electrode plate and a starting end of a negative electrode plate positioned at the innermost of the wound type cell each are provided with a blank current collector, the blank current collector is a part of the current collector, each surface of the part is not coated with an active material layer. One end of a positive electrode tab is directly welded to the blank current collector of the positive electrode plate and the other end of the positive electrode tab extends to the outside of a packaging bag about 10 mm. One end of the negative electrode tab is directly welded to the blank current collector of the negative electrode plate and the other end of the negative electrode tab extends to the outside of the packaging bag about 10 mm. If the electrode tab (i.e. the positive electrode tab or the negative electrode tab) is too thin, the strength of the electrode tab will be lower, the portion of the electrode tab that extends to the outside of the packaging bag will be broken easily, and an overcurrent sectional area of the electrode tab will be smaller, therefore, in order to ensure the strength and the overcurrent sectional area of the electrode tab, the thickness of the electrode tab is generally 60 μm or more. A thickness of an area where the electrode tab is welded is the maximum thickness in the wound type cell due to this superimposed thickness of the electrode tab, and because the thickness of the electrode tab is difficult to decrease further, the energy density of the cell is difficult to promote further.
In the existing battery structures, the positive electrode tab is welded to the current collector (i.e. the bank current collector) of the positive electrode plate by ultrasonic welding and the negative electrode tab is welded to the current collector (i.e. the bank current collector) of the negative electrode plate by ultrasonic welding, it needs to bond adhesive tapes above both sides of a part where the electrode tab (i.e. the positive electrode tab or the negative electrode tab) and the current collector are welded together, and the positive electrode tab and the negative electrode tab extends to the outside of the packaging bag after they are sealed by the packaging bag.
Therefore, the problem existing in the existing process is:
1. The thickness of the electrode tab is larger, so the electrode tab occupies a larger space of the cell in a thickness direction;
2. It needs to bond adhesive tapes above the both sides of the part where the electrode tab and the current collector are welded together, so the adhesive tapes also occupy a larger space of the cell in thickness direction;
3. Due to the larger thickness of the electrode tab, it has to use a bigger welding head to achieve ultrasonic welding, which leads to deeper uneven points formed on the current collector.